This invention relates to a fuel enrichment arrangement for a marine propulsion unit, and more particularly to a device for controlling the air/fuel mixture ratio during the starting period for an outboard motor.
An air-fuel ratio is the ratio of air to fuel mixed by a charge forming device of an engine. A low ratio of air to fuel is known as a rich mixture of fuel, while a high ratio of air to fuel is known as a lean mixture. Under a great many operating conditions, rich mixtures are less efficient during combustion. However, the rich mixture is desirable during cold weather and during starting conditions.
A charge forming device is placed on an engine to mix the air and fuel in the correct proportion (ratio) for various operating conditions. In order to achieve smooth starting for an engine, it has been known to make the air-fuel mixture richer by increasing the fuel feed rate at the carburetor without changing the air feed rate. This has been done by using a positive temperature coefficient (PTC) ceramic heater; such as in combination with a choke valve or enrichment valve. Specifically, when the engine is started, the PTC heater causes a valve to open for a predetermined period of time so that a fuel-rich air-fuel mixture is fed to the engine. Traditionally, the power source for the PTC heater has included a battery in combination with a relay.
As a result of the construction employing a battery, just described, such a known starting arrangement cannot be used with marine propulsion units which have no battery. Even if such a known system could be used with a marine propulsion unit, the device is complicated since it has been the common practice to provide a relay in the circuit in order to energize the PTC heater simultaneously with the turning of the starter switch to the "ON" position.
It is, therefore, a principle object of this invention to provide an improved starting arrangement for a marine propulsion unit.
It is another object of this invention to provide a starting arrangement which has a relatively simple construction and which can be used with propulsion units which do not have batteries.